The present invention relates to switching circuits, and in particular, to the use of magnetic induction in switching circuits to determine what type of magnetic field, namely in what polarity, will be the target for detection on the basis of environmental conditions.
In recent years, magnetic induction switching circuits using a magnetic inductor as the main body have been widely used in such fields as position sensing and rotation sensing. For instance, inside the upper or lower body of a cellular phone, the magnetic induction switching circuit is set up to detect the distance between the upper body and the lower body, and the sensed result is used as the basis for power control.
FIG. 1 is a magnetic induction switching circuit as used in the known technology. The magnetic induction switching circuit 10 may comprise a Hall Effect integrated circuit (Hall IC) 100, amplifier 110, Schmitt trigger circuit 120 and transistor 130. In the operation of the magnetic induction switching circuit 10, Hall IC 100 detects the presence of a magnetic field and generates a potential difference on the two terminals thereof on the basis of the magnetic flux. The electric potential difference as delivered on the two terminals of Hall IC 100, after being amplified through amplifier 110, will further be processed by Schmitt trigger circuit 120. If the amplified electric potential difference is larger than a default (e.g., a predetermined threshold) circuit 120 will generate an output to control the conduction of transistor 130.
However, this type of magnetic induction switching circuit in initial design can only respond to the change of a magnetic field with fixed polarity. Therefore, with regard to the system design manufacturers, a magnetic field with a specific polarity must be selected. Otherwise, the assembled system will not be able to operate in a normal way.